The present invention relates to a sheet handling device containing: a sheet support plate made of a heat conductive material having a first heat capacity, said plate having at least one cavity formed between a top wall defining a top surface of the plate and a bottom wall defining a bottom surface of the plate; and a temperature control system including a circulating system for circulating a temperature control fluid through the cavity.
In the copying and printing industry, a temperature controlled sheet support plate is frequently used for supporting an image receiving sheet and at the same time controlling the temperature thereof. For example, in a hot melt ink jet printer, a sheet, e. g. a sheet of paper, is advanced over a sheet support plate while the image is being printed. At room temperature, the hot melt ink is solid, and it is therefore necessary that the ink is heated in the printer above its melting point, before it can be jetted onto the paper. The ink droplets that have been jetted onto the paper tend to spread-out more or less before the ink solidifies. In order to obtain a suitable and constant amount of spreading of the ink droplets, the temperature of the sheet support plate and hence the temperature of the paper should be controlled such that the ink cools down at an appropriate rate.
In the initial phase of the print process, when a new sheet has been supplied, it is generally desirable to heat the sheet and to keep it at a suitable operating temperature. However, in the further course of the print process, it is necessary to dissipate the heat of the ink that solidifies on the paper. To that end, a temperature control fluid, e. g. a liquid, may be passed through the cavity in the plate in order to control the temperature of the plate.
Moreover, in order to obtain a good print quality, the surface of the sheet support plate should be perfectly flat, at least in the region where the image is being printed. Thus, the support plate should have a sufficient strength so that it will not bend under mechanical or thermal stress. As a result, the plate must have a certain minimum thickness, and this implies a certain minimum volume of the cavity.
For reasons of power consumption, it is required that the printer enters into a so-called sleep mode, when the printer is not operating for a certain period of time, and in the sleep mode, among others, the heating system for the sheet support plate is switched off. As a result, when a new image is to be printed, it will take a certain amount of time until the sheet support plate can be heated to its operating temperature.